The term lipid metabolism refers to the in vivo process of catabolism (decomposition) and anabolism (accumulation) of lipids, which are mainly triglycerides derived from food, and is intended to include, in the broad sense, reactions for transforming lipids into energy, biosynthesis of fatty acids, biosynthesis of acylglycerol. phospholipid metabolism, and cholesterol metabolism [Akira Misaki, Biochemistry for Nutrition, Asakura Shoten (1993), p. 123-134].
In recent years, mortality from adult diseases, particularly cardiovascular disorders, is rapidly rising, and a correlation between occurrence of such disorders and cholesterol concentration in blood has been pointed out. Some attempts have so far been made to lower the cholesterol concentration in blood by the use of specific food components. For example, the following proteins are known as proteins which lower the cholesterol concentration in blood: whey protein [Agric. Biol. Chem., 55, 813 (1991)]; soybean protein [Atherosclerosis, 72, 115 (1988)]; milk serum protein (Japanese Published Unexamined Patent Application No. 176713/93); and soybean protein hydrolyzate [J. Nutr., 120, 977 (1990)].
It is also known that egg yolk phospholipid lowers the cholesterol concentration in blood [Agric. Biol. Chem., 53, 2469 (1989)].
An attempt has been made to lower the cholesterol concentration in blood by the use of a combination of lactalbumin, collagen, soybean protein, or wheat gluten, and soybean lecithin (0, 2.5 and 5%) [Nutr. Rep. Int., 28, 621 (1983)].
Also known is a method for lowering the cholesterol concentration in blood by the use of a textured soybean protein containing 6% of soybean lecithin [Ann. Nutr. Metab., 29, 348 (1985)].